Harry Redknapp has emerged as the favourite to succeed Sam Allardyce, who was sacked yesterday by Newcastle United. It is understood that Portsmouth, Redknapp's current team, will receive an official approach from the Tyneside club today. He boasts an impressive CV and would offer the bonus of introducing the free-flowing football which was anathema to Allardyce.

Alan Shearer, holidaying in Barbados, has effectively ruled himself out of contention. It appears that Mike Ashley, Newcastle's billionaire owner, was not willing to take a gamble on someone as inexperienced as the former Newcastle and England captain.

Allardyce had always maintained that he would require "three to five years" to prove a success at St James' Park, but after less than eight months in the job he was deemed a failure last night. Shortly after holding a press conference at the club's training ground during which he had expressed satisfaction at the board's endorsement of his transfer-window plans, he was sacked.

Although the official line was that the 53-year-old manager had left the club by "mutual consent", Ashley, who had not appointed him, and Chris Mort, the chairman, had ruthlessly contradicted reports that they wanted to give him until at least the end of the season to prove his worth.

The former Bolton Wanderers manager, who had signed a three-year contract last summer, had yesterday talked optimistically of having "reached a turning point" but by then the boardroom bullets must already have been loaded, and last night thoughts switched to the identity of his successor.

Shearer had let it be known that, should a vacancy arise, he would be interested in the job, and in Barbados he has been socialising with Freddy Shepherd, Newcastle's former chairman, but by last night he had distanced himself from the vacancy. After initially refusing to comment, sources close to him said he was "very happy" as a Match of the Day pundit and it was "extremely unlikely" that he would be taking over at St James' Park.

Instead there was a rush of betting on Redknapp, whose Portsmouth side won 4-1 at Newcastle in November, although Mark Hughes, in charge of Blackburn Rovers, is also a viable candidate. This season Hughes signed a contract extension at Ewood Park after he was rumoured to have caught Ashley's eye. Newcastle's target is believed to be British and in work, which would appear to rule out the former Tottenham head coach Martin Jol.

Mort, who has placed Nigel Pearson, Allardyce's assistant, in caretaker charge and indicated he would be acting manager at Manchester United on Saturday, said: "Mike [Ashley] and I would like to place on record our thanks for Sam's efforts and wish him well for the future."

Allardyce said last night: "I am shocked and very disappointed but I wish the club all the best for the remainder of the season and for the future." It is quite a fall from grace for a man who had led Bolton into the Uefa Cup and hoped to succeed Sven-Goran Eriksson as England manager. Ironically Allardyce, who took over from Glenn Roeder only days before Ashley bought the club from the Hall family, had presided over Newcastle's best beginning to a Premier League season for a decade, but results rapidly deteriorated.

A watershed came in the form of the toxic abuse Allardyce received from the crowd during a 3-0 home defeat to Liverpool in late November. It signalled widespread disillusionment among fans, and a Boxing Day reverse at Wigan was punctuated by chants of "Shearer, Shearer" from the away end. Standing among them, Ashley will have taken note before, it seems, opting for a man boasting a proven managerial track record.

Dismayed by Allardyce's tactics, few Newcastle supporters took to the brand of direct, percentage football with which he had enjoyed relative success at Bolton. The team's players were understood to be similarly disaffected with both the manager's playing philosophy and tough, sports science-based training regime.

There have been only eight wins this season, the last one coming at Fulham on December 15, by which time even Allardyce must have privately wondered if he would see out the season.